(1) Field of the Invention
The present invention relates to a process for the preparation of polyvinylene sulfide.
(2) Description of the Prior Art
Polyvinylene sulfide is a sulfur-containing primary polymer having structural units represented by the formula --CH.dbd.CH--S.sub.n, and it has inherent electical and thermal properties and is valuable as an organic polymeric semiconductor or as an electric or electronic material.
Polyvinylene sulfide is a kind of the known polyvinylene chalcogenide. As the process for the preparation of this polymer, Ser. No. 471,152 ( hereinafter referred to as "prior application") proposes a process comprising reacting an ethylene dihalide with sodium sulfide in a solvent at a temperature of 60.degree. to 250.degree. C.
However, according to the process of the prior application, the yield is low and occurrence of thermal decomposition reaction or other side reaction is conspicuous. Furthermore, it often happens that the formed polymer contains therein an undesirable structure. For example, when dichloroethylene is reacted with sodium sulfide at an elevated temperature higher than 80.degree. C. in N-methyl-2-pyrrolidone as the solvent, the amount of formed polyvinylene sulfide in the obtained product is small and a salient amount of sulfur is formed. From the results of the gel permeation chromatography analysis, it has been found that the amount of the polymeric substance contained in the product is small.
As is seen from the foregoing description, in the process of the prior application, the yield and purity are low because of occurrence of thermal decomposition reaction and side reaction and the unstability of the starting monomer, and therefore, improvements have been desired.